With the varied composition of gaskets available on the market today, it is important that you use the proper sealant to ensure the gaskets seal effectively and not adversely affect the gaskets’ longevity. In many cases, using the correct sealant will actually extend the life of the gasket because it offers protection from engine heat as well as resistance to corrosive chemicals found in oils, fuels and other fluids that can cause the gasket to deteriorate over time.

There are literally thousands of sealants available on today’s market, and we are not recommending one brand over another, but certainly Permatex is an industry leader, and many of the product characteristics for each type of sealant reflect equivalency to the Permatex standards, so we will use their standards as a guide. A careful examination of what each category of sealants does and doesn’t do should point you in the right direction when deciding which type of sealant you should use. Here are just a few of the basic groups of sealants enthusiasts should have on hand when tackling an engine, transmission, differential or minor repair.

Shellac - Often referred to as Indian Head after the Permatex product. Shellac is ideal for thin paper or cardboard gaskets that are mounted in a low temperature and/or low pressure environment. It should not be used in temperatures higher than 300 to 350 degrees. Resistant to engine fluids, its most common uses are in mounting thermostat, timing cover or differential cover gaskets. They are not resistant to many shop chemicals, thankfully, because they can be a real bear to clean off, if necessary in the future.

High Tack - Available in brush-top bottle or in tubes, High Tack is a non-drying gasket sealant that can be used in similar applications to shellac, but can sustain temperatures of up to 500 degrees. It remains tacky and also resists kerosene, propane and diesel fuels.

Form-a-gasket sealers - These are available in several types: fast drying, fast hardening (usually called #1); slow drying, non-hardening (usually called #2); brushable slow drying, non-hardening (usually referred to as aviation or #3). All three form-a-gasket sealers are rated to 400 degrees, but each serves a slightly different purpose. Number 1 is most often used in applications you hope to never have to deal with again. It is often used to install block expansion plugs, threaded connections and to seal between metal-to-metal flanges. Number 2 sealants work best on cork gaskets or paper oil pan gaskets. Because they are non-hardening, clean-up is much easier when resealing is eventually needed. They are often used on neoprene transmission pan gaskets as well. Aviation form-a-gasket has the advantage of being brushable, so you can lay on a thin or thick coat to seal metal flanges, machined surfaces and solid gaskets. It works well for sealing hose connections because it is fuel and oil-resistant. It is also non-hardening for ease of resealing.

Copper gasket sealant - Available both in brushable and in aerosol forms, copper gasket sealer is fast-drying, and the metal content suspended within the sealant helps to dissipate heat and promote even heat transfer between the mating surfaces. It can also be used to fill small imperfections in the metal surfaces, promoting a more positive seal. Rated for up to 500 degrees, copper gasket sealant is best suited for cylinder head and exhaust manifold gaskets. It is also very easy to clean, even after extended periods of time.

Anaerobic sealers - Usually in a tube and red in color, anaerobic sealers are designed to be used in applications where outside air is not available to help the drying process. They were created to meet OE manufacturers’ requirements for a non-corrosive gasket maker in metal-to-metal applications. Anaerobic sealers are good for side-of-the-road leak repairs or for places where there never has been a gasket or the replacement gasket is no longer available. Anaerobic sealers will also fill small imperfections in mating surfaces.

RTV Silicone Sealers - Available in about a dozen different colors and spreadable via tubes, aerosol cheese-whiz-type cans or even in caulk-gun cartridges, Room Temperature Volatile silicone is effective as a gasket sealer as well as a gasket by itself. Temperature ratings and individual properties are available on a chart on the Permatex website. Basically, for applications up to 500 degrees, blue, black and grey are recommended. For up to 650 degrees, orange or red are recommended, and copper is good for temperatures up to 750 degrees. Whenever faced with a choice between a conventional RTV and an “Ultra” RTV, you should also consider that the Ultra products are sensor-safe for newer electronic-controlled vehicles.

Hylomar - This is a relatively new product in the aftermarket but has been used by many OE manufacturers for almost 30 years. It is a polyester urethane-based gasket compound that withstands temperatures of up to 500 degrees without hardening. It’s non-setting and remains tacky, making repeated disassembly and re-assembly much easier for racing applications where constant adjustments under the hood are necessary. It can be used as a gasket sealer or in place of a gasket. Hylomar could very well be the adjustable wrench of gasket sealers, fit for any do-it-yourself or professional tool box.

64 Responses to “Tech 101 – How to use the right gasket sealants”

I remember back in ’77 (or ’78) when GM came out with ‘GMS’ silicone sealer. If you ordered a valve cover gasket for a 350, you got a tube of that reddish smelly stuff instead of the traditional cork gaskets. It sure was effective but miserable to remove from the valve covers and heads.

When silicone bath tub sealer came out in the early ’70s it was a godsend to those of us with English motorcycles. We could actually park our bikes and NOT have them mark their spot. Of course that only lasted a short time until they came out with more specialized sealers.

The type of sealant used is more often based on the composition of the gasket, the environment it is being used in and the permanent the seal will be. Cork, Rubber, paper, neoprene, steel, ceramic, copper or combinations of these materials are all used on the gaskets you mention.
Personally, I have used #1 for steel head gaskets and permanent paper gaskets, #2 for cork and non-permanent paper, Copper for copper head gaskets, Aviation or RTV for neoprene and rubber. I found the hylomar to be quite effective on paper gaskets that have a bead of RTV already painted on them. I use ultra copper RTV in the absence of a gasket.

A nice refresher for those of us who grew up with “Pa” using “ackenpuckey”, with the aromatic smell of aviation form-a-gasket wafting around the basement garage. a few notes from my decades of experience:

Altho I am actually credited with developing the use of high-temperature [red] silicone for furnace and boiler retrofit applications, I’ve used it extensively in automotive applications as well, with good results. Two notes:
1. You do NOT over-use it! It takes only the barest film to make a good seal; I’ve seen motors RUINED because some moron glommed on, say, grey silicone sufficiently to block an oil passage or even interfere with water circulation.
2. The difference between the red and orange is that the red out-gasses [corrosive] acetic acid while curing, like all RTVs do, whereas they’ve somehow prevented this in the orange. Acetic acid will also attack copper and other corrosion-susceptible materials, especially if it’s in an application where it’s sealed tight with no chance to ventilate.
[BTW When Dow-Corning first put these out in the 60's we were told RTV stood for Room Temperature Vulcanizing]

I think modern sealants are far superior to the old Permatex/Indian Head form-a-gaskets, except in one critical application – form-a-gasket seems to be far more resistant to gasoline, whereas say, silicones will be affected to the point of uselessness by petrol exposure.

I agree about Permatex #1 aka “concrete in a tube”, about as bitchy a sealant to remove as they come. But why not consider some of Permatex’s thread sealer offspring, such as stud and bearing mount, or wet sleeve liner sealant? easier to use, and somewhat easier to remove if need be. [But you'll need heat with stud 'n bearing]

Anyway, this article, combined with one on thread sealants, should be printed off and put in every workshop “go to” ring binder – you DO have one of those, don’t you?

John, thanks from the basement of our 103 year old house for all your work. I am amazed I’m not more brain-damaged from all the chemicals we used in the 50′s and 60′s to keep cars running and clean. Anyone else remember carbon tetrachloride? On our Hudson’s we actually used Hi-Tack on head gaskets, and were usually rewarded with easy removal on subsequent repairs. My modern cars in some cases actually recommend no gasket – only red RTV. Which, was referred to as “room temperature vulcanization” when it was introduced. Semantics.

RTV is “Room Temperature Vulcanizing” and always has been. “Volatile” gives the impression that it is somehow dangerous at room temperature. Semantics generally refers (these days) to two ways of saying the same thing. There’s nothing at all the same about vulcanization and volatility.
And what’s new about Marston “Hylomar”? I was using Hylomar Blue for gaskets almost 25 years ago. I still have an old tube of it in the toolbox.

Any application calling for Permatex Grey is better served with a product available at Honda dealers called Hondabond. It’s far easier to work with during application and cleanup, but works exactly the same way. It does seem to be more easily removable after hardening, as well.

Hate to tell you but Honda is int he car making business not RTV silicone business. The Hondabond is good, but I’ll bet you a large sum of money that it is Permatex Ultra Grey or possibly Loc-Tite Grey RTV. The Loc-Tite products cost a little more than Permatex and I can’t definitively say they are better but I have always had good luck with Loc-Tite. So don’t buy Hondabond every again, you are only buying a rebranded product.

I have a racing fuel cell that I have a problem with the -12 AN fitting leaking where it installs in the hole. The cell is aircraft plastic with a slight wrinkle finish on the outside surface. The hole is slightly too close to the inner bottom curvature to seal with a gasket or o-ring where there is a smooth surface. Replacing the cell is problematic as it seems the race car was built around it. Which product will be best to seal this up?

Blue Devil is good for a temporary fix if installed correctly. You have to drain the cooling system and add the sealer with plain water, then add antifreeze back in after the sealant has done its job. Pretty expense stuff as is the Bars Leak nano-tech sealer. But both are compatible for aluminum and plastic intakes, so it could work in theory.

Bars Leak 1109 liquid copper is great stuff, but I would recommend the aluminum version, part number 1186. Your ’03 Buick had an aluminum core/plastic tank radiator, 1186 would be more compatible with the metallurgy of your engine and cooling system.

I am restoring a ’64 Pontiac Bonneville. Now before anyone jumps down my throat about proper terminology, this is my first build with my Dad seeing me along the way. We purchased a new tank for it and the opening of the tank to where the sending unit bolts onto is slightly damaged. It is not 100% flat and once the sending unit was bolted on, it leaked gas from the bolts. We used RTV to first seal under the sending unit where it lays against the metal tank. I also made round gaskets out of rubber gasket material for the washers and bolts. Hoping it all would seal, letting it set and dry, we realized it most likely would be inaffective with gasoline. What liquid gasket/barrier would seal this issue properly considering its contact with gasoline? I don’t want to buy a new tank and sending unit.

Thanks for the reply. I am doing the oil pan gasket on a 99 Jeep Cherokee Sport with the 4.0L six cylinder. Folks have a very hard time keeping the gasket in place when trying to re-install the pan. Any suggestions would be much appreciated.

Electric water pump by Proform leaking where metal hose adapter screws into the base of the pump. Tech said to use Indian Head, but did not specify what type. He said to apply it to the threads kg the adapter. Can you help on which type I should use?

Great write-up. I just overhauled a Tremec T-176 4 speed Jeep CJ tranny and I’m wondering what the best gasket sealer is to use along the top cover and the rear transfer case adapter along with the paper gaskets that came with the kit. I used “real thin” layer red Perma on the front input shaft (still not sure if that was a good idea), but I’m reluctant to use it for the rear and the top cover. When I dismantled the tranny, it appeared that a sort of varnish sealer was used previously, but it was all flaky and didn’t look original or effective. I figured I’d ask here as there’s not consensus in the forums I searched.

Tremec uses anaerobic RTV red in applications where there is no gasket or a rubber gasket is used, but, if you want a thin skin film over a paper or metal gasket, you should use the spray copper sealant. Anaerobic is preferred as an RTV because it will cure without exposure to air. Hylomar is also effective on thin paper gaskets.

Aren’t RTV and Anaerobic basically the opposite forms or sealant. By definition an anaerobic sealer cures without the prersence of air. RTV stands for Room Temperature Vulcanizing as was previously mentioned, clearly “room temperature” here means in the presence of air. The RTV has to pull moisture out of the air to cure whereas anaerobic sealers such as Loc-Tite 515 will not cure in the presence of air or at “room temperature” so to speak. Please correct me if I’m wrong?

This depends on the gasket being used. If it is a flat paper, we recommend red, orange or copper RTV. If the gasket has a bead of sealer around the parts already, number 2 sealer can be used on the non-beaded side or hylomar. The beaded side should not need any sealer. On classic cars with a cookie sheet intake gasket, copper spray sealant or number 2 will work fine. Proper torque on the manifold bolts will make just about any sealant much more effective.

I have a very slow leak on my timing chain cover. I was thinking either permatex spray sealant leak repair or black ultra RTV. The area is hard to get to directly so I am going to spray some brake cleaner into a vinyl tube and then use compressed air to blast it into the area. If I used the spray sealant I would be forced to stick the red spray stick into a vinyl tube as well, in irder to direct it into the leak. My concern with RTV is that is will not stay on well….. But would be. Uh easier to apply into the section leaking. Any thoughts? Thanks!!!

Good idea… Thanks for that! Does any specific RTV have a better chance of sticking well and preventing the oil from getting through? I have Ultra black but is seems ultra blue might have better oil resistance. Many thanks!

Hi, I drive a Vauxhall Corsa ‘C’ (2003) as is called in UK. Car may have different name in US. However, problem many of these ‘C’s develop is rain/water leak into the driver footwell (don’t forget, driver side is right hand side in UK!) causing sodden carpets and if left untreated, even mushrooms! The cause of majority of these leaks is down to perished seal of brake servo attached to bulkhead under the bonnet. Instead of having to remove great deal of items to gain access to brake servo and replace seal, is there an item as discussed/advertised on this page that comes in spray can/aerosol form with a directional spray that would do the job sufficiently enough instead of having to go to the lengths only a qualified mechanic could! Many thanks for consideration and any forthcoming responses.

Permatex makes a spray sealant leak repair in a 9-oz can that should be of use to you. seals low pressure leaks in rubber hoses, pan gaskets, plastic reservoirs, aluminum tubing and PVC pipe. Permatex part number is 82099. I believe this product supercedes both their original radiator hose clear shellac sealant and gas tank spray shellac sealant.

my replacement ACDelco water came with a metal gasket that has a rubber flange around the inside edge and around bolt holes. Do I use a sealant with this gasket? I was thinking of applying a thin coat of Ultra Black.What do you recommend?

Best info I have found. I have acquired an old Stihl chainsaw and have a new gasket for the cover to the gas tank/oil reservoir compartment. It appears to be thick paper with a plastic coating on the side towards the gas and oil. The tank/case is metal and the cover has a small ridge that sinks into the gasket. Should I use a sealant on the gasket and if so, what will work best with the oil and gas? Thanks.

you don’t want a very thick coating of anything on that edge, if that is where it is sealing. Hylomar should do the trick or I often use the amber dual weatherstrip adhesive. Both are impervious to fuel/oil/ethanol and non-permanent, should you have to remove the gasket again.

HI, I just replaced the high pressure hose for the pwr steering on a Nissan quest. the connection from the hose to the rack and pinion has a o-ring but is not making a good seal. what would be a good sealant to use. I was thinking about using Form-a-gasket number 1. I hope to seal it and not to mess with it anymore.

If it’s the banjo bolt that’s leaking you might try some high pressure thread sealant such as loc-Tite 545 or 567 but if it’s the hose with the 90* fitting and the small o-ring on the end you may have assembled it incorrectly. Also be sure to always put a little grease on o-rings.

Bought a new cast aluminum water pump and it is dripping antifreeze out of a small area between the heater hose fitting and where it goes into the water pump. Any thoughts on how to fix this leak? Tired ultra copper and it did not work

I’m replacing a cork gasket with a rubber one, to go between two metal surfaces that will contact brake fluid. What should I put on the rubber before assembly, if anything? Was going to use some copper coat I have, but instructions say not to use this on rubber. Will aviation cement be okay?

I have a Ford 2.3 turbo that I just installed in a Pinto. I had a pinched hose which would not allow the engine to properly vent under boost and it appears that the oil forced its way past the pan gasket. I’m trying to decide whether to go with a one piece rubber gasket like what is in there now, or go with a standard type cork gasket with the rubber ends. I’ve read other posts about these engines pushing oil thru gaskets and some use a sealer along with the gasket. Any recommendations? I have to drop the pan, fairly accessible, but would like to do it once….

stick with the one-piece neoprene oil pan gasket but install with a finger film of oil or use only as much sealer as is necessary to hold it in place while tightening the pan bolts. Use a thin sealer that is easily removed such as Hylomar or some of the number 2 gasket sealant. I would be afraid to use RTV because of the thickness of the film and the possibility some of it might pinch off into the pan during installation. RTV is good stuff, but it can be hell in an oil pan once it firms up.

I am replacing the intake manifold gaskets on my 2000 Cadillac Escalade. I have several different kinds of gasket sealants, however I have Permatex black silicone 16B that is already opened. Can it be used on the front and back of the manifold or should I use a high temp red rtv silicone type 650 made by Versa Chem. I also have Permatex high temp rtv 26C both unopened.

16B RTV black is rated for 450 degrees, I wouldn’t take the chance on an intake manifold. It is such a PITA to pull it apart again. Ultra Black is rated to 550, you should be OK with that, but the high-temperature Red is rated to 650. I’d feel better using the highest temperature stuff I had available.

I have to replace a gasket between the resevoir and the master cylinder. I’m worried about brake fluid being too aggressive. The resevoir is plastic and of course iron for the master cylinder…and im assuming before I pull it apart that its leaking due to rust…but its not made anymore. Which one should I use?

as we mentioned above, the only sealant advertising to be impervious to brake fluid is seal-all. Again, I would stick with the Permatex 54560 hydraulic sealant or cut a thin neoprene gasket from bulk material and use no sealant. Sometimes you can get away with slitting a piece of the red neoprene vacuum tubing and trimming the upper metal edge of the reservoir. That should take up any imperfections caused by pitting.